Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

• Integers in each row are sorted in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

Example:

Consider the following matrix:

[  [1,   4,  7, 11, 15],  [2,   5,  8, 12, 19],  [3,   6,  9, 16, 22],  [10, 13, 14, 17, 24],  [18, 21, 23, 26, 30]]

Given target = 5, return true.

Given target = 20, return false.

class Solution {public:    bool searchMatrix(vector
     
      
        > &matrix, int target) {        if (matrix.empty() || matrix[0].empty()) return false;        if (target < matrix[0][0] || target > matrix.back().back()) return false;        int x = matrix.size() - 1, y = 0;        while (true) {            if (matrix[x][y] > target) --x;            else if (matrix[x][y] < target) ++y;            else return true;            if (x < 0 || y >= matrix[0].size()) break;        }        return false;    }};